Anesthetic, cardiorespiratory, and metabolic effects of four intravenous anesthetic regimens induced in horses immediately after maximal exercise.

This research study aimed to evaluate the anesthetic, cardiorespiratory, and metabolic effects of four different intravenous anesthetic protocols in Thoroughbred horses that experienced intense physical exercise. The tested protocols demonstrated varying results, with some proving to have better effectiveness and safety when inducing anesthesia in the horses.

Research Method

The research study involves:

• A selection of six adult Thoroughbred horses that were preconditioned by exercising them on a treadmill.
• The horses underwent four simulated races with a minimum rest period of 14 days in between.
• Aiming to replicate optimal race conditions, each race was designed to cause the horses to operate at 120% of their maximal oxygen consumption.
• The duration of each race was capped at a maximum of 2 minutes or until each horse shows signs of fatigue.

Anesthetic Regimens

Five minutes after each race, the horses received one of the four following intravenous anesthetic combinations:

• ketamine hydrochloride (2.2 mg/kg)
• ketamine (2.2 mg/kg) and diazepam (0.1 mg/kg)
• tiletamine hydrochloride-zolazepam hydrochloride (1 mg/kg)
• guaifenesin (50 mg/kg) and thiopental sodium (5 mg/kg)

The administration of these anesthetic regimens was randomized among the horses.

Data Collection and Results

Throughout the procedure, several aspects were closely monitored and recorded:

• Cardiopulmonary indices, or data related to heart and lung function, were recorded, and blood samples were collected both before and at specific intervals for 90 minutes after each race.
• A thorough comparative analysis showed that every regimen led to the induction of lateral recumbency, a state of anesthesia where the horse lies on its side.
• The quality and duration of anesthesia varied among the regimens, with anesthesia induced after ketamine administration being noted as significantly worse than the other methods. Additionally, ketamine resulted in a significantly shorter duration of anesthesia.
• Time to lateral recumbency was found to be significantly longer following the administration of ketamine or guaifenesin-thiopental, versus ketamine-diazepam or tiletamine-zolazepam.
• Differences were also observed in terms of arterial blood pressures. Those post the administration of guaifenesin-thiopental were significantly lower than pressures recorded after the other anesthetic combinations were administered.

Conclusion

From the above findings, the researchers concluded that anesthesia can be safely induced in horses shortly after maximal exercise. The combination of ketamine-diazepam and tiletamine-zolazepam appears to be the most effective and safe, inducing good quality anesthesia with minimal disruption to cardiopulmonary and metabolic functions. The remaining two regimens, ketamine alone, and guaifenesin-thiopental, were not recommended due to their less favorable effects.